We all know that the capacitor voltage cannot be changed and the inductor current cannot be changed. So, what is the theoretical basis?
Below, take the RC first -order low -pass filter as an example to briefly explain the reason for everyone.

1. Why can't the capacitor voltage be changed?
VIN charges the capacitor C1 through the R1 resistor, and VIN's potential is added on the two metal pole plates of the capacitor C. Under the influence of the influence of the electrostatic charge, the positive and negative charges gather to the two polar plates of the capacitor to form an electric field. This is the charging process of capacitors.

The number of charge charging capacitance is q, Q = CV, and C is constant, so the number of charge is positively proportional to the voltage.
C = Q/V, capacitance represents the ability of capacitor storage charge. The differential expression is:

The current is the change in the number of charges during the unit time:

Based on (1) and (2) two formulas to get:

It can be seen from the formula that the current and voltage changes in the capacitor are proportional. In other words, the voltage of the voltage on the capacitor is proportional.
Assuming that the voltage of the capacitor can change, that is, the infinite current is required. In fact, there is no infinite current, that is, the voltage voltage cannot be changed.

2. Why can't the inductive current change?
The sum of the magnetic flux of each turning chain of the inductance coil is called the magnetic chain ψ, which measures how much the inductive coil is mass -powered.
The magnetic chain is proportional to the current. The larger the current, the more the inductive coil is charged, that is, ψ = L*i. For the specified inductor coil, L is a constant.
L = ，/i, the amount of inductance represents the electromagnetic conversion ability of the inductor coil. The differential expression is:

According to the principle of electromagnetic induction, the magnetic chain changes generate an inductive voltage. The larger the magnetic chain change, the higher the response voltage, that is:

Based on (1) and (2) two formulas to get:

It can be seen from the formula that the changing rate of inductor voltage and current is directly proportional. In other words, the change rate of current and inductance voltage is proportional.
Assume that the current of the inductance can change, that is, the infinite voltage is required, and it does not exist in actual situation, that is, the inductive current cannot be changed.

Article Source: 21IC Electronic Network Public Account